Internucleotide phosphate analogs have recently gained interest as having uses in and of themselves, other than for making recombinant DNA for application in genetic engineering techniques. For example, methanephosphonate linked deoxyoligonucleotides inhibit viral replication in mammalian cells (Smith, C. C., et al., Proc. Natl. Acad. Sci. U.S.A. 83, 2787-2791 (1986)) and some phosphorothioates have been shown to have anti-HIV activity (Matsukura, et al., Proc. Natl. Acad. Sci. U.S.A. 84, 7706-7710 (1987)). Internucleotide phosphate analog linkages, such as the phosphoramidate linkages, are useful as an attachment for reporter groups, intercalating agents and cross-linking agents. Such linkages also can be resistant to certain nucleases which would otherwise act upon naturally-occurring phosphate internucleotide linkages. Moreover, the modification of the phosphorus-containing internucleotide linkages has been shown to affect gene expression (Marcus-Sekura, et al., Nucl. Acids Res. 15, 5749-5763 (1987)). Therefore, there is a continuing interest in phosphate analogs for all of these utilities, as well as for use in synthesizing sequence-defined oligonucleotides and analogs thereof.